View single post by Esprit2
 Posted: 02-16-2020 07:27 pm
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Joined: 05-01-2005
Location: Minneapolis, Minnesota USA
Posts: 512
No, 0.0003" isn't a lot of wear in a shim, and they can be re-used with considerably more wear... a deeper pocket. They're almost new... consistant with only being run 3000 miles since the last rebuild.

> If I use the sims I will flip them over.

NO ! When you re-install USED shims, the dimple must go back DOWN against the valve stem. The stem will correctly fit into the pocket a stem created. A tappet's flat inside surface will bridge across a pocket, not touch the bottom of the pocket where you measured, and give an incorrect clearance (incorrect = not matching your calculations).

> It looked like black sealant was used for the cam housing to the head but it turned out to be a black gasket.

Very early J-H 907s used a thin gasket between the cam carriers and the head. A Tech Service Bulletin eliminated that gasket back in the day (early-mid 1970's) when Jensen was still in business, and all 907s should have been converted to gasketless long, long ago. The modification involved cutting a counter-bore around the oil passages at the front, between the head and carrier, so it's not a simple matter of deleting the gasket. An O-ring is to be installed in the counter-bores during assembly. Inspect your cylinder head. There should be a counterbore around the base of what looks like a hollow dowel pin. If it's not there, we can talk then.

Deleting the gasket will result in the cam carriers sitting lower on the head by it's thickness. That will change all the shim thicknesses by the same amount. Have you just shimmed 'GASKETLESS' ?

> I believe there was a coolant leakage at onetime.

Well, that's not good. You'll have to get to the bottom of that issue.

> I checked the toque on the head nuts and they were at the top end of the spec or greater.

What torque spec are you using? The spec given in the J-H Workshop manual is not appropriate for use with any modern composite head gasket.... Lotus or aftermarket clone. Similarly, the original 907 head studs can NOT handle the torque for the modern gaskets. Replace the head studs with either Lotus 1993-onward B-prefix studs (B907ExxxxX), or with aftermarket ARP studs. Each stud option has it's own specific torque spec.

The B-prefix studs look pretty much like the original studs, except that they have a semi-spherical dimple machined into their top ends. The ARP studs are black.

Q1 - Yes, it's okay to use an assembly lube on the sides of the shims as you describe; However the mess would be difficult to control through multiple trial runs (you will only rarely hit alll the correct clearances in one try). The official approach is to buy small bar magnets and apply them to the tops of the tappets... the side-cheeks that stick out past the cam lobe. Then the shims will stick to the tappets when you lift the cam carrier off.

In a running engine, all the surfaces of the tappets and shims get coated with oil, and that's what sticks the shims to the tappets in the first place. When I assemble the bits for a trial run while shimming, I lightly oil the top sides of the tappets... just a drop on a finger tip, and smear the tappets that are already in the spring retainers.

As you have already experienced, the tappets will come off with the cam carrriers/ tappets, but won't stick there forever. When I remove the cam carriers, I pull & rotate inverted in one smooth move. You have no choice but to go straight up off the studs at first, but then immediately rotate the carrier inverted. One smooth motion that shouldn't take more than a second.

Q2 - Lotus discontinued the original steel-asbestos-steel head gasket (S-A-S) in Jan 1993. To the best of my knowledge, the S-A-S gasket is no longer available from any non-Lotus sources.

Lotus' replacement gasket has a crushed thickness that is 0.5 mm (0.020") thicker, which lifts the head off the block by a similar distance, reducing the compression ratio by about half a point. The stock J-H 8.4:1 compression ratio becomes 7.9:1. "IF" your engine has 9.5:1 pistons, their compression ratio is now 9.0:1.

There are aftermarket clones of the Lotus composite gasket (at least one, maybe two). Very recently, I have been looking into whether the clone gasket's crushed thickness is the same as Lotus' gasket, but so far I don't have an answer. There's also some question if Cometic has a gasket that might have a different crushed thickness, but again, no answer yet. It's even possible that a Cometic gasket is one of the clone gaskets. Again, I'm just getting into that 'investigation'.

If you wish to get the engine put back together now, Then you don't have any current gasket option that mimics the original S-A-S thickness. Your 9.5: compression will end up somewhat lower.

There is a solution, but it won't be cheap, and will require a complete engine re-build. From Jan 1993, Lotus milled the block deck lower by the same amount that the new gasket was thicker. (0.5 mm) then set the liners deeper into the block by the same amount in order to maintain the correct Nip. You could take your bare block to a machine shop and have the same thing done to it. Short of that, your compression ration will drop about half a point when the modern head gasket is installed. Period.

Q3 - Every cam manufacturer/ re-grinder has their own way of marking their cam products. I have no idea what to tell you about where to look for them all.

A 'LOTUS' cam will have a A907ExxxxX part number cast into the body of the cam. That's the blank's number, and all Lotus cams used the same blank. After they're ground, another ID is added to the smooth front shank that you can see between the front of the cam carrier and the back of the cam pulley.

C-Cam = smooth, no mark
D-Cam = one groove cut all the way around the shank
E-Cam = two grooves
104 Cam = 4444444.... stamped all the way around
107 Cam = 7777777... all the way around.

For any of the other aftermarket cams, you would have to ask the seller or manufacturer. I've got no clue.

Use a caliper to measure the total height of the cam lobe... the total egg shape from top to bottom. Then measure cross-wise to that to get the base circle diameter. Subtract to get the lobe lift. That will give you some clue whether the cam in the engine is stock, or something else.

C-Cam = 0.340" - Stock J-H cam.
D-Cam = 0.350"
E-Cam = 0.344"
104 Cam = 0.410"
105 Cam = 0.433" - Lotus, Competition only, No longer available.
106 Cam = 0.450" - Lotus, Competition only, NLA.
107 Cam = 0.252"
108 Cam = 0.460" - Lotus, Competition only, NLA.
DS2 Cam = = 0.415"
Dave Bean BLL-107 = 0.375"
Dave Bean BLL-104 = 0.420"
Dave Bean BLL-105 = 0.425"
Kent Cams BD4 = 0.431" = Cosworth BD4
Kent Cams L14 = 0.415" = Cosworth L14
Kent Cams L1 = 0.408" = Cosworth L1

Q4 - Get the engine together, then do a compression test. J-H & Lotus both used the 8.4:1 compression ratio, but J-H spec'd a cold compression test, and Lotus spec'd a hot test. They give different results. You can do a cold test on a non-functional engine, but a hot test is more representative of the engine's true operating condition... what's your priority?

8.4:1 cr - 7.58 - 8.96 bar .. (110 - 130 psi) COLD = Jensen-Healey CR Test Spec
8.4:1 cr - 10.2 - 11.6 bar .. (150 - 170 psi) HOT = Lotus CR Test Spec

9.5:1 cr - 11.2 - 12.6 bar .. (165 - 185 psi) Hot = Lotus only, J-H never used 9.5:1
9.44:1 cr - 11.2 - 12.6 bar (165 - 185 psi) Hot = Lotus only, 912LC
10.9:1 cr - 11.5 - 13.0 bar (170 - 190 psi) Hot = Lotus only, 912HC

7.5:1 cr - 8.8 bar (130 psi min) Hot = Lotus only, 910 Turbo prior to 1986
8.0:1 cr - 9.5 bar (140 psi min) Hot = Lotus only, 910 Turbo 1986-96

When doing the test, run the engine long enough to get up to full operating temperature (except JH, room-temp cold), hold the throttles fully open, and crank the engine at a minimum of 200 rpm until the pressure reading peaks and holds at a max value. In order to facilitate the fastest cranking rpm practical, remove all spark plugs, make certain the battery is fully charged, or use jumper cables to a running vehicle. If there's fuel in the system (ie, the engine is in running condition), then disconnect the ignition to minimize the risk of fire with the spark plugs removed (some fuel mist will spew from the cylinders with no sparkplugs installed).

If the engine is in good condition (no other problems that could produce low compression readings), then the above range of pressures should give you an idea of your engine's current compression ratio.

Tim Engel